In European Patent application 239,476 there were described .gamma.-carboline derivatives of general formula: ##STR3## in which R.sub.1 and R.sub.5 are, among others, hydrogen atoms, R.sub.2 may denote a hydrogen atom or a hydroxyl or alkoxy radical, R.sub.3 and R.sub.4 are especially alkyl radicals and n equals 2 to 4, which exhibit an antitumor activity.
Furthermore, other pyridoindole derivatives have been described in the literature by C. Ducrocq et al., J. Het. Chem., 12 (5), 963 (1975) or by Ch. S. Lee et al., Heterocycles, 16 (7), 1081 (1981), but no therapeutic activity is mentioned.